Electrolytic cell



G. C. GAUT El' AL ELECTROLYTIC CELL Filed Feb. 28, 1938 ATTORNEY Feb. 13, 1940.

Patented Feb. 13, 1940 UNITED STATES ELECTROLYTIC CELL Geoffrey Charles Gant, Romford, and David John Pritchard Phillips, Croydon, England, assignors to P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Application February 28, 1938, Serial No. 193,191 In Great Britain October 19, 1937 4 Claims.

This invention relates to improvements in electrolytic condensers and like cells.

An object of the invention is to provide improved conductive spacers for' use between electrodes -of devices of this character.

Other objects'of the invention Will be apparent;

from the following description taken in connec- Figure 1 illustrates a step in making the-spacers of the present invention;

Figure 2 shows another step in producing one embodiment of the invention;

Figure 3 illustrates a condenser assembly embodying the spacers of the present invention; and

Figure 4 shows a completed condenser.

According to one feature of this invention a dry spacer which requires no impregnation, may if desired be manufactured independently of any other step in the process of manufacture of the cell, may be readily reeled or otherwise handled mechanically, and may be stored without difliculty, is manufactured by forming a solution of a suitable cellulose derivative, adding thereto at least one ionogen and at least one high-boiling liquid which is not a solvent for the cellulose derivative, and casting or otherwise treating the resulting mixture to produce a sheet, film or the like of the requisite` dimensions; the solvent is wholly or partially removed at this last stage.

According to another feature of the invention a spacer is prepared by the steps specified in the preceding paragraph with the exception that the ionogen and high-boiling liquid are partially or Wholly combined, prior to their addition to the solution of cellulose derivatives, to form a reactiond product. l

In either case the mixture is conveniently, but not essentially, ca'st 'as a film in continuous lengths on a travelling bend or rotating drum, the surface of which must be such as to avoid detrimental effects on the mixture; the dry film is stripped therefrom by any suitable means such as those known in the art of casting cellulosederivative films and the casting machine may be similar in all respects to those employed-in that art; Alternatively the mixturemay be cast on one of the cell electrodes, which is preferably (Cl. F15-315)' previously etched, or on a band of non-absorbent gauze, e. g. sized gauze, which acts solely as a mechanical stiifener and is not impregnated by the mixture.

The term suitable cellulose derivative is to be understood to exclude derivatives which product corrosion of the electrodes upon decomposition, such as nitrocellulose, and those which contain free sulphates or chlorides. The preferred derivative is cellulose acetate but ethyl cellulose and cellulose aceto-butyrate may be mentioned as suitable alternatives. The solvent is preferably a low-boiling solvent such as acetone, methyl acetate or ethyl formate but a solvent of higher boiling point than these, such as `ethylene glycol diacetate, may be used provided that vit is one that evaporates more quickly from the mixture during casting than the high-boiling liquid; two or more of these solvents may, of course, be used simultaneously.

The ionogen may be one or more of the acids used in the formation of conductive compositions for electrolytlc condensers, such as citric or boric v gradient, preferably an organic borate compound ,e

such as` amyl borate, to give a plasticproduct, and/or a ller such as shellac or colophony resin.

In some cases the mixture may be cast hot but it is usually desirable to arrange matters so that it can be cast cold, the advantage of this being that subsequent detrimental absorption of water is reduced or avoided.

Example I.A dope is prepared by dissolving 450 grams of cellulose acetate in 31/2 litres of acetone andthe following mixed ingredients are then added tothe dope:

Grams Amyl borate 350 Ethylene glycol 75C Glycerine 15G Citric acid 80 Ammonium borate 250 The mixing of these ingredients may be accelerated if desired by heating to a temperature of 75 to 80 C. They are added slowly to the dope with vigorous stirring by stirring means which are inert as regards the mixture, i. e. cause no reaction and do not dissolve. Rods of glass, aluminum or stainless steel are suitable.

'I'he mixture thus obtained is preferably nltered and de-aerated either by heating, e. g., in a container surrounded by hot water, or by suction in order to avoid the formation of bubbles during casting. I'he mixture is cast hot, e. g., at a temperature of 70 to 80 C.' for a linear casting band speed of 2 ft. per minute, the band being preferably of aluminum or stainless steel. If a band of nickel, copper or other material having detrimental effects on the mixture is required to be used it must be provided with a protective layer, e. g. of benzyl cellulose. The greater part of the acetone is given up by the mixture at this stage. The thickness of the film may be from two to three thousandths of an inch.

An operating economy may be obtained by arranging to recover the acetone given off in the casting operation.

The cast mixture must be used quickly if atmospheric conditions are such as to offer the risk of undue absorption of water.

Example II.--A composition as specified in the above example is used with the addition of 320 grs. of distilled water, the water being added to the ve ingredients tabulated prior to their incorporation in the cellulose acetate dope. This modied mixture can be cast cold, giving a product which is less prone to the absorption of atmospheric moisture than a mixture which is cast hot. Filtering and de-aerating of the mixture may be effected prior to casting.

Example IIL-A mixture is prepared as in Example I except that 100 grs. of shellac are added to the cellulose acetate solution before the addition of the remaining five ingredients.

Example IV.-A mixture is prepared from the following ingredients:

(1) Cellulose acetate grams 450 (2) Amyl borate do 350 (3) Dlethylene .glycol -do '750 (4) Glycerine do 150 (5) Ammonium borate do.. 600 (6) Ethylene glycol do 450 (7) Citric acid d0 250 (8) Distilled water do 300 (9) Acetone litr`es 6 Ingredients 3, 4, 5 and 6 are first mixed together and heated at 135 C. for twelve hours to give a reaction product. 'Ihis product has added to it ingredient 2 with vigorous stirring and then the solution obtained bymixing ingredients 'I and 8 is added. Finally the resulting mixture while still hot (at '75 to 80 C.) is added to the dope formed by mixing ingredients 1 and 9. The nal mixture is cast hot as described with reference to Example I.

Referring to the drawing Figure 1 shows the step in the manufacture of the spacers wherein band IU is passed through one of the mixtures II heretofore described so as to receive a lm I2 of the mixture which is allowed to dry thereon. The band l0 may be a metal band used merely for the purpose of casting the film I 2 in which case the film is subsequently stripped off, as by blade I3, as shown in Figure 2, and rolled up into a roll I4 for subsequent use.

In other cases band I0 may be the intended condenser electrode itself, preferably etched, in which case the lm I2 is allowed to remain as a coating on the electrode in the nshed condenser. In still other casesv the band I0 may be a strip of sized cloth, as described, which serves as a base for the completed spacer.

Figure 3 shows a condenser assembly comprisand advantages has been described herein asA carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. A film-maintaining spacer for dry electrolytic condensers comprising a non-tacky, nonhomogeneous, porous matrix of cellulose derivative selected from the group consisting of cellulose acetate, ethyl cellulose and cellulose acetobutyrate, and an ionogen and a high boiling liquid intimately embodied therein, said ionogen being at least one of the materials selected from the group consisting of acids used in the formation of conductive compositions for electrolytic condensers and the stable salts thereof, and said high boiling liquid being selected from the group' consisting of glycerine and the glycols.

2. A spacer for dry electrolytic condensers comprising a cellulose derivative selected from the group consisting of cellulose acetate, ethyl cellulose and cellulose aceto-butyrate, and an electrolyte comprising an ionogen and a high boiling liquid embodied therein, said cellulose derivative comprising a non-tacky, non-homogeneous, porous matrix carrying said electrolyte, said spacer being capable of maintaining a current-blocking film on a condenser electrode during operation of the condenser with said spacer interposed between the electrodes thereof.

3. The method of making a non-tacky, nonhomogeneous, porous conductive film-maintaining spacer for dry electrolytic condensers which comprises dissolving a cellulose derivative selected from the group consisting of cellulose acetate, ethyl cellulose and cellulose aceto-butyrate, at least one ionogen and at least one high boiling liquid which is not a solvent for,the cellulose derivative in a volatile solvent, and forming a sheet spacer therefrom by evaporating said volatile solvent from a thin layer thereof.

4. The method of making a non-tacky, nonhomogeneous, porous conductive nlm-maintaining spacer for dry electrolytic condensers which comprises dissolving the following ingredients in a common volatile solvent: (1) a cellulose derivative selected from the groupI consisting of cellulose acetate, ethyl cellulose and cellulose aceto-butyrate, (2) at least one ionogen selected from the group consisting of acids used in the formation of conductive compositions for electrolytio condensers and the stable salts thereof and (3) at least one high boiling liquid selected from the group consisting of glycerine and the glycols, and forming a sheet spacer therefrom by evaporating said volatile solvent from a thin layer thereof.

GEOFFREY CHARLES GAUT. DAVID JOHN PRI'I'CHARD PHILLIPS. 

